Cuda program for multiplication of two matrices

                 For Cuda multiplication using shared memory, check Next Post. 

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                 In this post of "Cuda program for multiplication of two matrices", I have considered two cases:
1. Two dimensional blocks and one thread per block.
2. One block and two dimensional threads in that block.




1. Two dimensional blocks and one thread per block.

#include<stdio.h>
#include<cuda.h>
#define row1 2 /* Number of rows of first matrix */
#define col1 3 /* Number of columns of first matrix */
#define row2 3 /* Number of rows of second matrix */
#define col2 2 /* Number of columns of second matrix */

__global__ void matproduct(int *l,int *m, int *n)
{
    int x=blockIdx.x;
    int y=blockIdx.y;
    int k;
  
n[col2*y+x]=0;
for(k=0;k<col1;k++)
   {
    n[col2*y+x]=n[col2*y+x]+l[col1*y+k]*m[col2*k+x];
   }
}

int main()
{
    int a[row1][col1];
    int b[row2][col2];
    int c[row1][col2];
    int *d,*e,*f;
    int i,j;

    printf("\n Enter elements of first matrix of size 2*3\n");
    for(i=0;i<row1;i++)
    {
        for(j=0;j<col1;j++)
            {
                scanf("%d",&a[i][j]);
            }
    }
    printf("\n Enter elements of second matrix of size 3*2\n");
        for(i=0;i<row2;i++)
        {
            for(j=0;j<col2;j++)
                {
                    scanf("%d",&b[i][j]);
                }
        }

    cudaMalloc((void **)&d,row1*col1*sizeof(int));
    cudaMalloc((void **)&e,row2*col2*sizeof(int));
    cudaMalloc((void **)&f,row1*col2*sizeof(int));

 cudaMemcpy(d,a,row1*col1*sizeof(int),cudaMemcpyHostToDevice);
 cudaMemcpy(e,b,row2*col2*sizeof(int),cudaMemcpyHostToDevice);

dim3 grid(col2,row1);
/* Here we are defining two dimensional Grid(collection of blocks) structure. Syntax is dim3 grid(no. of columns,no. of rows) */

    matproduct<<<grid,1>>>(d,e,f);

 cudaMemcpy(c,f,row1*col2*sizeof(int),cudaMemcpyDeviceToHost);
    printf("\nProduct of two matrices:\n ");
    for(i=0;i<row1;i++)
    {
        for(j=0;j<col2;j++)
        {
              printf("%d\t",c[i][j]);
        }
        printf("\n");
    }

    cudaFree(d);
    cudaFree(e);
    cudaFree(f);

    return 0;
}

Output:

 Enter elements of first matrix of size 2*3
1 2 3 4 5 6

 Enter elements of second matrix of size 3*2
7 8 9 10 11 12

  Product of two matrices:
 58    64   
139    154   

2. One block and two dimensional threads in that block.

#include<stdio.h>
#include<cuda.h>
#define row1 2 /* Number of rows of first matrix */
#define col1 3 /* Number of columns of first matrix */
#define row2 3 /* Number of rows of second matrix */
#define col2 2 /* Number of columns of second matrix */

__global__ void matadd(int *l,int *m, int *n)
{
    int x=threadIdx.x;
    int y=threadIdx.y;

    int k;

n[col2*y+x]=0;
  for(k=0;k<col1;k++)
   {
    n[col2*y+x]=n[col2*y+x]+l[col1*y+k]*m[col2*k+x];
   }
}

int main()
{
    int a[row1][col1];
    int b[row2][col2];
    int c[row1][col2];
    int *d,*e,*f;
    int i,j;

    printf("\n Enter elements of first matrix of size 2*3\n");
    for(i=0;i<row1;i++)
    {
        for(j=0;j<col1;j++)
            {
                scanf("%d",&a[i][j]);
            }
    }
    printf("\n Enter elements of second matrix of size 3*2\n");
        for(i=0;i<row2;i++)
        {
            for(j=0;j<col2;j++)
                {
                    scanf("%d",&b[i][j]);
                }
        }

   cudaMalloc((void **)&d,row1*col1*sizeof(int));
    cudaMalloc((void **)&e,row2*col2*sizeof(int));
    cudaMalloc((void **)&f,row1*col2*sizeof(int));

 cudaMemcpy(d,a,row1*col1*sizeof(int),cudaMemcpyHostToDevice);
 cudaMemcpy(e,b,row2*col2*sizeof(int),cudaMemcpyHostToDevice);

dim3 threadBlock(col2,row1);
/* Here we are defining two dimensional Grid(collection of blocks) structure. Syntax is dim3 grid(no. of columns,no. of rows) */

    matadd<<<1,threadBlock>>>(d,e,f);

 cudaMemcpy(c,f,row1*col2*sizeof(int),cudaMemcpyDeviceToHost);
   
 printf("\nProduct of two matrices:\n ");
    for(i=0;i<row1;i++)
    {
        for(j=0;j<col2;j++)
        {
              printf("%d\t",c[i][j]);
        }
        printf("\n");
    }

    cudaFree(d);
    cudaFree(e);
    cudaFree(f);

    return 0;
}

Output:

 Enter elements of first matrix of size 2*3
1 2 3 4 5 6

 Enter elements of second matrix of size 3*2
7 8 9 10 11 12

  Product of two matrices:
 58    64   
139    154    

Next: Cuda program for matrix multiplication using shared memory


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